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Search: id:A129890
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| A129890 |
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Difference between the double factorial of the n-th nonnegative even number and the double factorial of the n-th nonnegative odd number. |
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+0
2
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| 1, 5, 33, 279, 2895, 35685, 509985, 8294895, 151335135, 3061162125, 68000295825, 1645756410375, 43105900812975, 1214871076343925, 36659590336994625, 1179297174137457375, 40288002704636061375, 1456700757237661060125
(list; graph; listen)
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OFFSET
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0,2
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FORMULA
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a(n)=(2*n)!!-(2*n-1)!!, with n>=1.
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EXAMPLE
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2!!-1!!=2-1=1
4!!-3!!=8-3=5
6!!-5!!=48-15=33
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MAPLE
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P:=proc(n) local a, i, j, k, w; for i from 1 by 1 to n do k:=product(2*j, j=1..i); w:=product(2*j-1, j=1..i); a:=k-w; print(a) od; end: P(20);
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CROSSREFS
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Cf. A122649.
Sequence in context: A087633 A135075 A049377 this_sequence A120733 A144792 A001828
Adjacent sequences: A129887 A129888 A129889 this_sequence A129891 A129892 A129893
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KEYWORD
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easy,nonn
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AUTHOR
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Paolo P. Lava & Giorgio Balzarotti (ppl(AT)spl.at), Jun 04 2007
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